The present invention relates to a swingable and slidable bed apparatus for use with the X-ray diagnostic device and the like.
When the alimentary canal and its related organs are to be diagnosed, an image forming agent having an X-ray absorption rate higher than that of the human body is used to take X-ray photographs of shapes of these organs. It is needed in this case that the image forming agent flows in the organs. The bed for use with the X-ray diagnostic device is therefore designed so that the patient horizontally lying on it can be shifted in posture to his standing normal or to his being fallen his head down. Bed 1 is therefore swung round the axis of rotation of support 2, as shown in FIG. 1.
The height of this type bed is preferably made so relatively low as to allow the patient to mount on it with easiness. When it is made low like this, it is also advantageous for the doctor to diagnose the patient lying on it, but it happens that floor 4 interferes with one end of it when it is swung. As shown in FIG. 2, therefore, it is slid, while being swung, parallel to that plane 5 of it on which the patient is lying, to prevent floor 4 from interfering with one end of it.
Guide rail 6 having rack 7 is attached to bed 1 along the upper rim thereof. Another guide rail 8 is attached to bed 1 along the lower rim thereof. Semi-circular gear 9 is rotatably supported by support 2. Cam followers 10 and 11 attached to semicircular gear 9 slide on guide rails 6 and 8. Pinion 13 is engaged with semicircular gear 9 and another pinion 12 is engaged with rack 7. Pinions 12 and 13 are respectively rotated at constant speed.
When pinions 12 and 13 are synchronously rotated, therefore, semicircular gear 9 is rotated while rack 7 is moved. As the result, bed 1 is slid parallel to plane 4 while being swung, as shown in FIG. 2. Because pinions 12 and 13 are respectively rotated at constant speed, the bed is swung while slid at constant speed (constant speed system). The bed is usually swung in a range of -90.degree. -+90.degree..
It is assumed in FIG. 2 that the amount of slide of the bed be denoted by S, the amount of maximum slide of the bed by Smax, the angle of swing (or inclined angle) of the bed by .theta., and the amount of elevation (or vertical component of slide amount) of the bed by V.
The relation among slide amount S, elevation amount V and swing angle .theta. is as follows. EQU S=(.theta./90.degree.).multidot.Smax (1) EQU V=S.multidot.sin .theta. (2)
When equation (1) is substituted by equation (2), EQU V=(.theta./90.degree.).multidot.Smax.multidot.sin .theta. (3)
The following can be understood from equations (1) and (3).
Slide amount S is proportional to swing angle .theta.. As swing angle .theta. is increased, slide amount S is also increased in proportion to swing angle .theta..
Elevation amount V is not proportional to swing angle .theta.. When swing angle .theta. is relatively small, elevation amount V is extremely small. When swing angle .theta.is relatively large, elevation amount V is relatively large. Namely, elevation amount V is increased as swing angle .theta. becomes larger and larger.
Further, the relation between the slide and the elevation amount can be understood from equation (2) as follows. When the swing angle is relatively small, the slide amount is extremely small in relation to the elevation amount. As shown in FIG. 3, for example, the slide amount is several times the elevation amount when swing angle .theta. equals to 30.degree.. When the swing angle is relatively large, the slide amount becomes substantially equal to the elevation amount. As shown in FIG. 4, for example, the slide and the elevation amount are substantially equal when swing angle .theta. equals to 80.degree.. When the slide amount is increased in a case where the swing angle is relatively large, therefore, the elevation amount is increased in corresponding with the amount of slide increased, but when the swing angle is relatively small, the elevation amount is increased a little even if the slide amount is increased.
When the swing angle is relatively small, therefore, the condition under which one end of the bed interferes with the floor can be improved better. The sliding speed of the bed is made higher with respect to the swinging speed of the bed in this case. When the swing angle is relatively small, the slide amount is thus increased rapidly to keep the elevation amount relatively large. When the sliding speed of the bed is made high, however, the slide amount becomes extremely large in a case where the swing angle is relatively large. Therefore, rack 7 of bed 1 comes out of pinion 12.
When the swing angle is relatively small, therefore, the sliding speed of the bed is made higher in relation to the swinging speed of the bed, while when the swing angle is relatively large, the sliding speed is made lower in relation to the swinging speed of the bed (speed change system), as shown in FIG. 5. The sliding speed is therefore changed two times relative to the swing angle. When the swing angle is relatively small, the slide amount is rapidly increased to keep the elevation amount relatively large, while when the swing angle is relatively large, the slide amount is not made extremely large. Maximum slide amount Smax is made equal to the maximum slide amount in the constant speed system (a driver means for this constant speed system is disclosed in an article "Swinging and Sliding of the Bed for Use with the X-ray Diagnostic Device" written by the inventor of the present invention for a magazine "Machine Designs" (Pages 66-71, December Edition, 1986) published by Nikkan Kogyo Shinbun).
However, this speed change system has such a drawback that horizontal component H of slide amount S becomes extremely large when swing angle .theta. is relatively small. Namely, the relation between this horizontal component H and slide amount S can be expressed as follows. EQU H=S.multidot.cos .theta. (4)
When equation (1) is substituted by equation (4), EQU H=(.theta./90.degree.).multidot.Smax.multidot.cos .theta. (5)
When the value of Smax is set large in a case where the swing angle is relatively small, therefore, horizontal component H is rapidly increased.
Namely, when the slide amount is increased in a case where the swing angle is relatively small, elevation amount V is hardly increased but horizontal component H is rapidly increased, as apparent from equations (2) and (4). As the sliding speed is made higher and higher, therefore, the increasing ratio of horizontal component H becomes larger and larger.
When horizontal component H is made large like this in the case where the swing angle is relatively small, the traveling distance of the bed becomes long in the horizontal direction. As the result, the space in which the bed can be swung and slide becomes large.